Retail stores like Banana Republic or Gap include return labels and packaging with your online purchases, which makes returns a breeze. Some people use this policy to great effect, and will buy the same dress in multiple sizes and simply return the ones that don't fit. eBay is not like a retail website, for the most part you are not at liberty to return products if they don't fit or you don't like the colour. eBay returns will always suck, in regards to both time & money, for both parties.
Policies are at the complete discretion of the seller, and I can totally understand why they make most sales FINAL. The only time I went through a return process was when the seller shipped the complete wrong product. I was extremely annoyed at having to go to the post office and bother with it, even if I was refunded the postage. You have to ensure the package gets to point A to Point B, and when you consider international shipping and postal strikes, things can go missing; I know I've had a few items lost in transit. To avoid all that trouble, I've actually had a couple sellers who told me to keep the wrong item (for my trouble) and then sent me the replacement as well (worked out in my favour since both items were my size!).
You have to think of these purchases as Final Sale. This should make your buying practices more thoughtful and cautious. Be sure to read the listing a few times (i.e. the fine print) and know the sellers policies.